Jiaojun Zhu

Effect of gap size created by thinning on seedling emergency, survival and establishment in a coastal pine forest

It is desirable and necessary to preserve the continuity of a coastal forest through reasonable management because it can provide many shelter benefits through altering the wind behavior along the shore. Thinning is an undoubtedly important measure for the continuity of forests as it provides suitable conditions for natural regeneration; however, thinning increases the risk of wind damage immediately after thinning in the coastal areas. Therefore, few thinning study related to regeneration in a coastal forest has been made. In order to test whether coastal forest of Japanese black pine (Pinus thunbergii Parl.) requires a specific gap size created by thinning for regeneration and to compare seedling establishment among four thinning treatments, observations of emergence, survival and establishment of P. thunbergii seedlings, together with soil water content, litter, wind and light regime were made. The observations were conducted over four growing seasons in three sizes of circular gaps (the gap diameter to stand height ratios for the four gap sizes were 0.5, 1.0, 1.5 and 0.0, the control) corresponding to the four thinning treatments in Niigata shore, Japan. Results indicated that density of seedlings older than 1 year increased with gap size or canopy openness (OP). Seedling establishment was greater in 1.5 gap sizes than in any other gap sizes, while seedlings peaked near the west and north edges of the gaps but not in the gap centers exposed to direct solar radiation. Seedling growth in 1.5 gap sizes was also significantly higher than that in any others. A tendency of seedling height increasing from east to west edge and from south to north edge across the gap was observed. Only 1- or 2-year-old seedlings occurred in gap sizes of 0.0 and 0.5, therefore establishment in both gap sizes was considered as failing. The results imply that although P. thunbergii seeds can germinate in small gaps, even in under canopy, the seedlings are unable to survive. The seedlings apparently require a minimum gap size greater than or equal to 1.0, or OP >30% in order to survive, and may require at least gap size greater than or equal to 1.5, or OP >40% for further development into sapling. These results can be explained by the changes of microclimates, i.e. increase of light, soil water and airflow exchange, decrease of litter and canopy cover, and alleviation of the competitions for water in gaps created by thinning. Therefore, thinning strategy, especially patch-pattern thinning is potentially a viable silvicultural measure in management for the coastal pine forest. These results provide references for establishment and management of coastal P. thunbergii forests

Effects of drought stresses induced by polyethylene glycol on germination of Pinus sylvestris var. mongolica seeds from natural and plantation forests on sandy land

Effects of drought stresses induced by polyethylene glycol (PEG) (0.0%, 10%, 15%, 20%, 25%, and 30%, with four replicates) on germination of Mongolian pine (Pinus sylvestris var. mongolica) seeds produced in plantations (southern Keerqin sandy land) and natural forests (Hulunbeier sandy plain) were observed. The results indicated that the seeds from both provenances did not germinate when PEG concentration was more than 25%. The time of initial germination and that of its completion of stressed seeds from both provenances were delayed when compared with the unstressed seeds. The germination capacity and germination rate of natural seeds were significantly higher than those of plantation seeds for all treatment levels (P < 0.05). The mean growth rates of radicle and hypocotyl from natural seeds were significantly higher than those from plantation seeds at all treatment levels below 20% PEG treatment (P < 0.05). The ratios of radicle to hypocotyl of 20% PEG treatment were significant higher than those of the corresponding controls for both provenances (P < 0.05). These results suggested that Mongolian pine seeds/seedlings had stronger resistance to PEG drought stresses; 10% PGE stress did not significantly influence germination. Natural seeds exhibited more resistance to PEG stress than plantation seeds. It was concluded that drought stress on seed germination might be one cause of obstructed natural regeneration of Mongolian pine plantations on sandy land. It is recommended that natural seeds be used for afforestation, and light drought stress (e.g., 10% PEG stress) may be useful in improving seed germination and the growth of radicles and hypocotyls.

Effects of gaps on regeneration of woody plants: a meta-analysis

Forest gaps, openings in the canopy caused by death of one or more trees, have a profound effect on forest regeneration and drive the forest growth cycle. It is therefore necessary to understand the effects of forest gaps on regeneration for modern forest management. In order to provide a quantitative assessment of the effects of forest gaps on regeneration of woody plants, we conducted this review of gap effects on woody plant regeneration on the basis of 527 observations from 42 individual papers, and reported the results of these data in a meta-analysis. Overall, densities of regenerated woody plants were significantly greater (359%) in forest gaps than on the closed-canopy forest floor. The regeneration density in gaps of plantation forests was significantly greater (P < 0.05) than that of natural forest because the regeneration in gaps of plantation forests was improved by both gap effects and experimental measures. Similarly, in comparison to natural gaps, regeneration was better enhanced in artificial gaps. Regeneration density exhibited a significantly positive correlation with gap size, but a negative correlation with gap age because the gap size decreased with increasing gap age. Shade tolerance of woody plants affected regeneration density in gaps and understory. Average regeneration density of shade-tolerant species exhibited a significantly positive response to gaps but densities remained lower in total than those of intermediate and shade-intolerant species. Gap effects on regeneration decreased in response to increasing temperature and precipitation because of the limiting effects of lower temperature and moisture on woody plant regeneration. In summary, forest gaps enhance woody plant regeneration, and the effects of gaps varied by forest type, gap characteristics, environmental factors and plant traits. The results of this meta-analysis are useful for better understanding the effects and roles of gaps on forest regeneration and forest management.

Optical stratification porosity as a measure of vertical canopy structure in a Japanese coastal forest

Porosity of a forest stand is an important descriptor of vertical forest structure, although it is a difficult variable to define and measure because of its three-dimensional nature. Fortunately, studies on the effects of obstruction on irradiation in forest stands provide us with a method which uses a hemispherical photographic silhouette to estimate an alternative measure of porosity, here defined as optical stratification porosity (OSP). The differences between OSP and canopy closure, canopy cover and canopy gap, which are frequently used by ecologists and foresters, are discussed. The estimation of OSP of a forest stand using hemispherical photographic silhouettes is evaluated based on an analysis of stratification patterns in vertical forest structure. The OSP measured in a coastal pine forest having different thinning ratios is presented as an example to demonstrate the method. The results indicate that when the strata can be visually identified, the OSP can be obtained using hemispherical photographic silhouettes. Alternatively, if OSP is measured at various canopy heights in a forest stand continuously, the stratified vertical structure patterns of the forest stand can be determined. The predicted stratification of vertical forest structure based on the measurement of OSP can indicate the vertical strata more accurately than visual identification alone. Therefore, the estimation of OSP may be helpful in modeling wind profile, leaf area index, crown ratio and light inside a forest stand and may prove useful to those applications in which fine-scale vertical stratification is desirable.

Environmental impacts of the shelter forests in Horqin Sandy land, northeast China.

Assessing environmental effects of shelter forests is primarily necessary for realizing their greatest protective benefits. The Three-North Shelter Forest Program (TNSFP), the largest ecological afforestation program in the world, has been operated for three decades in China but so far lacks comprehensive assessment of its environmental impacts. Horqin Sandy Land (HSL) in Northeast China is one of the key areas in the TNSFP implementation. To identify the principal contributors to environmental changes in HSL, we evaluated impacts of variations in landscape features, shelter forest areas, climatic factors, and social factors on changes in sandy land areas from 1978 to 2007, by using Gray Relational Analysis. Our analysis showed that during the period 1978 to 2007, the sandy land area decreased by 3.9% in low aeolian dunes, 14.5% in low mountains and hills, and 98.9% in high elevation alluvial flats of HSL. Factors with Gray Correlation Degrees >0.9 were identified as the patch shape index (PSI) and the landscape isolation index (LII) of grasses in low aeolian dunes, PSI of grasses in mountains and hills, and area of broadleaved forests and LII of shrubs in alluvial flats. It is concluded that establishment of the shelter forests has played a significant role in controlling the expansion of sandy land in HSL. To sustain the long-term environmental benefits of the shelter forests in the remaining period for TNSFP construction, suitable tree species should be selected and planted at appropriate densities based on the local precipitation, groundwater and landform conditions, and the system stability of the total landscape.

Wind speeds within a single crown of Japanese black pine (Pinus thunbergii Parl.).

Abstract Wind speed and crown thickness, which is defined as a horizontal distance from the observed point to outer edge of a crown in windward direction, were measured within a normal crown of a single tree of Japanese black pine (Pinus thunbergii Parl.) at four vertical sections. Simultaneously, wind speed and direction were observed outside the crown. Regression analysis is used to obtain the wind profiles within the single crown. The results suggest that the crown features make a large influence on the wind profiles, therefore, the crown thickness as an indicator of crown feature is employed to develop the horizontal wind profile within the crown. A consistent relationship between relative wind speed and corresponding crown thickness is established for predicting wind speed at a horizontal plane. Additionally, vertical wind profile within the crown is also examined as literature suggested in exponential form. Within a single tree crown, where the distribution of leave and branch is essentially uniform with height, and the tree form is similar to Japanese black pine, the vertical wind profile can be derived from a single wind speed measurement outside the crown with using the parameter derived in this study. Based on the vertical and horizontal profiles, wind speed at any position in a plane within a crown at height z can be reasonably estimated if providing the crown thickness and wind data outside the crown. The wind profiles discussed here may be useful when discussing the ventilation of airflow at any level of a crown, analyzing the transfer processes for questions of disease and solving the problems of the tree damage by salty wind from the sea, etc.

The role of ectomycorrhizal fungi in alleviating pine decline in semiarid sandy soil of northern China: an experimental approach

The decline of Mongolian pine (Pinus sylvestris var. mongolica) trees on sandy land in northern China has caused serious ecological concerns. Mongolian pine is an ectomycorrhizal fungus (ECM)-dependent species. Three ECM species (Boletus sp., Lactarius deliciosus and L.sp.) were collected from Mongolian pine plantation stands to test their beneficial effects on Mongolian pine seedlings and their responses to environmental factors such as pH, drought stress and temperature. The results indicated that ECM inoculation significantly increased the rate of ECM colonization and the length of seedling shoots. The three ECM could grow in a pH range from 4 to 7, but did not grow under heavy drought stress (−1.53 MPa). High temperatures (over 37 °C) caused death of ECM. When related to soil pH, soil water content and temperature in the Mongolian pine plantations, water conditions and temperature were unfavorable for ECM growth in surface soil, but suitable in deeper soil. Therefore, it was concluded that the failure of natural regeneration in Mongolian pine plantations might be influenced by the lack of ECM in the surface soil because of high temperatures causing ECM death. Moreover, the majority of the root area is distributed in deeper soil, which alleviates the stresses on ECM development and arrests pine decline; this is beneficial for tree growth.RésuméLe dépérissement du Pin de Mongolie (Pinus sylvestris var. mongolica) sur les terres sableuses du nord de la Chine a causé de graves inquiétudes écologiques. Le Pin de Mongolie est une espèce dépendante de champignons ectomycorrhiziens (ECM). Trois espèces de champignons ectomycorrhiziens ont été récoltés (Boletus sp., Lactaria delicious et L. sp.) dans des plantations de Pin de Mongolie pour tester leur effet bénéfique sur des semis de Pin de Mongolie et leur réponse aux facteurs environnementaux tels que pH, stress hydrique et température. Les résultats indiquent que l’inoculation d’ ECM accroît significativement le taux de colonisation d’ ECM et la longueur des pousses des semis. Les trois ECM peuvent croître avec une gamme de pH allant de 4 à 7, mais ne peuvent pas se développer sous un stress hydrique important (−1,53 MPa). Des températures élevées (au dessus de 37 °C) causent la mort de ECM. Relativement au pH du sol, la teneur en eau du sol et la température dans les plantations de Pin de Mongolie, les conditions hydriques et la température étaient défavorables pour la croissance d’ ECM à la surface du sol, mais étaient appropriées dans un sol plus profond. Par conséquent, il a été conclu que l’échec de la régénération naturelle dans les plantations de Pin de Mongolie aurait pu être influencé par un manque d’ ECM en surface du sol car les températures élevées causent la mort des ECM. En outre, la majorité de la surface racinaire est répartie dans la profondeur du sol, ce qui réduit les contraintes au développement des ECM et arrête le dépérissement des pins, et est favorable à la croissance de l’arbre.

Mapping Spatial Distribution of Larch Plantations from Multi-Seasonal Landsat-8 OLI Imagery and Multi-Scale Textures Using Random Forests

The knowledge about spatial distribution of plantation forests is critical for forest management, monitoring programs and functional assessment. This study demonstrates the potential of multi-seasonal (spring, summer, autumn and winter) Landsat-8 Operational Land Imager imageries with random forests (RF) modeling to map larch plantations (LP) in a typical plantation forest landscape in North China. The spectral bands and two types of textures were applied for creating 675 input variables of RF. An accuracy of 92.7% for LP, with a Kappa coefficient of 0.834, was attained using the RF model. A RF-based importance assessment reveals that the spectral bands and bivariate textural features calculated by pseudo-cross variogram (PC) strongly promoted forest class-separability, whereas the univariate textural features influenced weakly. A feature selection strategy eliminated 93% of variables, and then a subset of the 47 most essential variables was generated. In this subset, PC texture derived from summer and winter appeared the most frequently, suggesting that this variability in growing peak season and non-growing season can effectively enhance forest class-separability. A RF classifier applied to the subset led to 91.9% accuracy for LP, with a Kappa coefficient of 0.829. This study provides an insight into approaches for discriminating plantation forests with phenological behaviors.

Monthly Air Temperatures over Northern China Estimated by Integrating MODIS Data with GIS Techniques

The Three-North Shelter/Protective Forest Programme (TNSFP), the largest ecological afforestation program in the world, was launched in 1978 and will last until 2050 to improve ecological conditions in the Three-Northregionsof China.Tomanagetheshelterforestssustainably, itisnecessarytoaccurately estimate air temperature on a large scale, but the spatial distribution of ground meteorological stations is limited. A hybrid method was established by combining stepwise regression modeling and spatial interpolation techniques (SRMSIT) to construct the monthly mean, minimum, and maximum air temperatures (Tmean, Tmin, and Tmax, respectively) at a 1km 3 1km grid size in the Three-North regions. Stepwise regression modeling was applied to construct the relationship between air temperatures (Tmean, Tmin, and Tmax—the dependent variables) and geographical and Moderate Resolution Imaging Spectroradiometer (MODIS) variables (the independent variables). Spatial interpolation techniques were used to correct the residual values. According to the factor analysis, three geographic (altitude, latitude, and continentality) and two MODIS variables[nighttimelandsurfacetemperature (LST)and normalized differencevegetationindex]were selected in stepwise regression modeling, and nighttime LST was the most powerful remote sensing variable. The SRMSIT method, in which the spatial interpolation of the residuals was done with inverse distance weighting, achieved average root-mean-square error values at 0.868 ,1 .108 ,a nd 1.138 Cf orTmean, Tmin ,a ndTmax, respectively. Therefore, the simple regression algorithms derived from the combination of remote sensing and geographical variables, together with residual interpolation techniques, have the potential to accurately estimate monthly air temperature in large regions.

A methodological approach for spatial downscaling of TRMM precipitation data in North China

Accurate precipitation data with high spatial resolution are crucial for many applications in water and land management. Tropical Rainfall Monitoring Mission (TRMM) data, with accurate, high spatial resolution are crucial for improving our understanding of temporal and spatial variations of precipitation. However, when used in the Three-North Shelter Forest Programme of China, the spatial resolution of TRMM data is too coarse. In this study, we presented a hybrid method, i.e. a regression model with residual correction method, for downscaling annual TRMM 3B43 from 0.25° to 1 km grids from 2000 to 2009. The regression model was applied to construct the relationship among TRMM 3B43 data, continentality (CON), and the normalized difference vegetation index (NDVI) under five different scales (0.25°, 0.50°, 0.75°, 1.00°, and 1.25°). In the residual correction, three spatial interpolation techniques, i.e. inverse distance weighting (IDW), ordinary kriging, and tension spline, were employed. The 1 km monthly precipitation was disaggregated from 1 km annual precipitation by using monthly fractions. Analysis shows that (1) CON was a good variable for precipitation modelling at large-scale regions; (2) the optimum relationship between precipitation, NDVI, and CON was found at a scale of 1.25°; (3) the most feasible option for residual correction was IDW; and (4) the final annual/monthly downscaled precipitation (1 km) not only improved the spatial resolution but also agreed well with data from 220 rain gauge stations (average R2 = 0.82, slope = 1.09, RRMSE = 18.30%, and RMSE = 51.91 mm for annual downscaled precipitation; average R2 = 0.41, slope = 0.79, RRMSE = 76.88%, and RMSE = 15.09 mm for monthly downscaled precipitation).